Molybdenum Sulphates

Reduction of a solution of molybdic acid in sulphuric acid by means of hydrogen sulphide is stated to yield the compound MoO₃.MoO₂.2SO₃ as a black substance, soluble in water to an unstable brown solution; reduction with alcohol is said to yield soluble blue crystals of the sulphate 7MoO₃.2MoO₂.7SO₃.aq.

The sulphate Mo₂(SO₄)₃.2H₂O has been described, but its existence has not been confirmed.

A compound of molybdenum trioxide with sulphur trioxide, MoO₃.SO₃, has, however, been obtained as deliquescent, soluble crystals when molybdenum trioxide is dissolved in warm concentrated sulphuric acid.

An oxysulphate, Mo₂0(SO₄)₂.xH₂O (x = 5 or 6), is formed as a green hygroscopic precipitate when an electrolytically reduced solution of molybdenum trioxide in sulphuric acid is poured into air-free acetone. The salt possesses strong reducing properties, liberating copper and silver from their salts and reducing ferric and mercuric compounds. The sulphate radical is precipitated by barium chloride only on warming. On heating, the oxysulphate decomposes according to the equation:

Mo₂O(SO₄)₂.xH₂O = Mo₂O₅ + 2SO₂ + xH₂O.

The compound Mo₃Br₄SO₄.3H₂O, a yellow powder insoluble in water, results from the interaction of molybdenum hydroxybromide, Mo₃Br₄(OH)₂, and sulphuric acid.